1. Field of the Invention:
The invention in general relates to sonar transducer arrays, and particularly to an improved assembly and mounting arrangement.
2. Description of the Prior Art:
Active or passive transducer arrays carried by surface or sub-surface vessels are utilized for detection of distant targets.
The arrays are made up of a multitude of transducer elements, each operable to provide an output signal in response to impingement of acoustic energy within the design frequency range of the element.
Beamformer apparatus carried by the vessel is responsive to all of the transducer element outputs to form one or more beams to obtain an indication of target bearing. In the case of an active system, target range may also be obtained.
In one type of passive system currently in use, a plurality of transducer elements are longitudinally arranged and embedded in a somewhat flexible elongated enclosure called a "biscuit" made of durable nitrile rubber. The individual transducer elements are positioned within individual cavities within the nitrile rubber and potted in place by means of, for example, polyurethane.
A backing means including a signal conditioning plate is mounted on, and generally conforms to the contour of, the carrying vessel below the water line thereof. A plurality of transducer carrying biscuits are, in turn, mounted relatively close to one another in side-by-side relationship on the signal conditioning plate to form the array.
In order to maintain exact positional relationships of the transducer elements, the biscuits are firmly bolted to the signal conditioning plate. In addition, in order to exclude the surrounding water medium form contacting the rear surface of the biscuits, they are also bonded to the signal conditioning plate such as with epoxy and the gaps between biscuits are filled in or sealed with a gap filler.
After the biscuits are bonded in place, there is no convenient way of inspecting the uniformity of the signal conitioning plate to biscuit joint. Any air gaps that might be present may seriously impair the proper operation of the array and, accordingly, the biscuit may have to be removed and re-bonded. In addition, if one or more transducer elements of the biscuit should have to be replaced, the entire biscuit must be removed.
The removal and subsequent replacement of a biscuit is an extremely time-consuming, labor-intensive and costly operation. To initiate a repair or replacement, the entire vessel must be placed in dry-dock or alternatively, the entire array must be removed necessitating the use of a large, heavy-duty crane since the entire array may weight many tons.
To remove an individual biscuit, the gap filler between it and adjacent biscuits must be removed. If the filler material is a potting compound, it must be cut away. Thereafter, nuts and bolts are separated and a lifting force is applied to one end of the biscuit so that the epoxy bond may be broken such as with a chisel. If the bolts holding the biscuit are welded to the signal conditioning plate, the task of chiseling is made that more difficult.
After the biscuit is free, any epoxy remaining on the signal conditioning plate must be removed such as by sanding or grinding after which a new coat of paint may have to be applied. After the paint is cured, which may be days, a new biscuit may be retrofitted by bolting and bonding in place and the vessel placed back into service only after the epoxy has cured.
The above labor-intensive process of replacing a biscuit can take a number of days before the vessel could be placed back into service. With the arrangement of the present invention, a defective hydrophone may be replaced in a matter of hours, or even minutes in situ without any requirement for the vessel being placed in dry-dock.